Bone fixation implant system and method

ABSTRACT

A system for performing bone arthrodesis includes an implant for bone arthrodesis and a bone fastening device. The implant includes a fastener with an elongated shaft having a head at one end and a bone-piercing point at the opposite end. A first washer has structure for engaging the head of the shaft so as to be polyaxially pivotable with respect to the head. A locking member has structure for engaging the shaft. The locking member can have a second washer pivotally engaged thereto. The bone fastening device can include an elongated cannula with a collet for detachably engaging the first washer and for advancing the first washer. Structure is provided for engaging the fastener and for advancing and rotating the fastener through the collet and through the first washer. The bone arthrodesis device further includes a lower end portion extending from the cannula. The lower end portion has structure for detachably engaging the locking member. The fastener, first washer, and locking member are aligned such that the advancing fastener will advance through the first washer, drill through the bone, and move into the locking member. A method for performing bone arthrodesis is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Utility patent applicationSer. No. 10/683,076, filed Oct. 10, 2003, which claims the benefit ofU.S. Provisional Application No. 60/417,543, filed Oct. 10, 2002.

FIELD OF THE INVENTION

This invention relates to bone arthrodesis, and more particularly tobone fixation implants and systems and methods for installing suchimplants.

BACKGROUND OF THE INVENTION

Bone arthrodesis or fusion is a process used to assist in the healing orstabilization of impaired bones or joints. In particular, facetarthrodesis is used to fuse the superior and inferior facet in spinaltreatment operations. Prior art systems and methods have used bonescrews which are screwed through the superior and inferior facets toimmobilize the joint so as to permit the adjoined bone sections to fusetogether. Wire has also been used to loop around the facets toimmobilize the joint. The surgical procedures that must be performed toimplant the screws or wires are difficult and time consuming. There istherefore a need for improved bone fixation implants, devices andmethods.

SUMMARY OF THE INVENTION

An implant for bone fixation comprises a fastener with an elongatedshaft having a head at one end and a bone-piercing point at the oppositeend. A first washer has structure for engaging the head of the shaft soas to be polyaxially pivotable with respect to the head. A lockingmember has structure for engaging the shaft. The locking member has asecond washer pivotally engaged thereto. The shaft and the lockingmember can have cooperating threads. The locking member can be a nut.The second washer can be pivotally attached to the nut by a clip.

The first washer and second washer can comprise angled contact surfaces.The contact surfaces can be serrated. One of the head and the firstwasher can have a convex surface. The other of the head and the firstwasher can have a cooperating concave surface. The convex surface is incontact with the concave surface to provide for polyaxial pivoting ofthe first washer with respect to the head. The first washer can comprisestructure for engagement to a bone fastening device. The structure cancomprise a circumferential groove that is adapted to receive a flange onthe fastening device. The first washer can comprise rotationalengagement structure. The rotational engagement structure can comprisedepressions adapted to receive protrusions on a fastening device.

The locking member can comprise structure for engaging the fasteningdevice. The structure can comprise depressions adapted to receiveprotrusions on a lower end portion of the fastening device.

A bone fastening device according to the invention can have an elongatedcannula with a collet for detachably engaging a first washer and foradvancing the first washer. The fastening device can further comprisestructure for detachably engaging a fastener and for advancing thefastener through the collet and through the first washer. A lower endportion extends from the cannula. The lower end portion can havestructure for detachably engaging a locking member. The fastener, firstwasher, and locking member are aligned such that the advancing fastenerwill advance through the first washer, through the bone, through thesecond washer and into the locking member.

A system for performing bone arthrodesis includes an implant for bonefixation and a bone fastening device. The implant includes an elongatedshaft having a head at one end and a bone-piercing point at the oppositeend. A first washer has structure for engaging the head of the shaft soas to be polyaxially pivotable with respect to the head. A lockingmember has structure for engaging the shaft. The locking member can havea second washer pivotally engaged thereto. The bone fastening device caninclude an elongated cannula with a collet for detachably engaging thefirst washer and for advancing the first washer. Structure is providedfor detachably engaging the fastener and for advancing the fastenerthrough the collet and through the first washer. The bone fasteningdevice further includes a lower end portion extending from the cannula.The lower end portion has structure for detachably engaging the lockingmember. The fastener, first washer, and locking member are aligned suchthat the advancing fastener will advance through the first washer,through the bone, through the second washer and into the locking member.

A method for performing bone arthrodesis includes the steps of providingan implant for bone fixation, the implant comprising: a fastener with anelongated shaft having a head at one end and a bone-piercing point atthe opposite end; a first washer having structure for engaging the headof the shaft so as to be polyaxially pivotable with respect to the head;and a locking member having structure for engaging the shaft. Thelocking member can have a second washer pivotally engaged thereto.

The method further includes the step of providing a bone fixationdevice, the bone fixation device comprising: an elongated cannula havinga collet for detachably engaging the first washer and for advancing thefirst washer, and structure for engaging said fastener and for advancingthe fastener through the collet and through the first washer; a lowerend portion extending from said cannula, said lower end portion havingstructure for detachably engaging the locking member. The fastener,first washer, and locking member are aligned such that the advancingfastener will advance through the first washer, through the bone,through the second washer and into the locking member.

The method further includes the step of positioning the bone fixationdevice with the bone between the cannula and the lower end portion. Thedevice is operated to advance the first washer to the bone. The deviceis then operated to advance the fastener through the first washer, thebone, and into the locking member.

BRIEF DESCRIPTION OF THE DRAWINGS

There is shown in the drawings embodiments which are presentlypreferred, it being understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown,wherein:

FIG. 1 is a perspective view of a bone fastening device according to theinvention.

FIG. 1 a is a perspective view of a bone fastening device having aprotective cannula.

FIG. 2 is a side elevation of a bone arthrodesis implant according tothe invention.

FIG. 3 is a side elevation of a fastener.

FIG. 4 is a perspective view.

FIG. 5 is a side elevation of a locking member and washer assembly.

FIG. 6 is a perspective view.

FIG. 7 is a perspective view, partially in phantom.

FIG. 8 is a perspective view of a first, superficial washer.

FIG. 9 is a bottom perspective view.

FIG. 10 is a bottom perspective view of an alternative embodiment.

FIG. 11 is a bottom perspective view, partially broken away.

FIGS. 12 a-c are cross-sectional views, partially broken away, showingalternative orientations.

FIG. 13 is a perspective view of a collet.

FIG. 14 is a schematic side elevation view showing a first mode ofoperation.

FIG. 15 is a schematic side elevation view showing a second mode ofoperation.

FIG. 16 is a schematic side elevation, partially broken away andpartially in cross-section.

FIG. 17 is a schematic perspective view, partially broken away.

FIG. 18 is a schematic perspective view in a second mode of operation.

FIG. 19 is a schematic perspective view, partially in phantom, in asubsequent mode of operation.

FIG. 20 is a schematic perspective view in yet another mode ofoperation.

FIG. 21 is a schematic cross-sectional view.

FIG. 22 is a schematic cross-sectional view illustrating a finalinstallation.

FIG. 23 is a schematic perspective view showing bone fixation utilizingan implant according to the invention.

FIG. 24 is a schematic cross section illustrating a bone fixation systemand method, in a fist mode of operation.

FIG. 25 is a schematic cross section illustrating a second mode ofoperation.

FIG. 26 is a schematic cross section illustrating a third mode ofoperation.

DETAILED DESCRIPTION OF THE INVENTION

There is shown in FIG. 1 a bone fastening device 10 according to theinvention. The device 10 has a main body 12 and an elongated housing 14terminating in a lower end portion 16. The device 10 has structure forholding a first washer 20 at a distal portion of the elongated housing14 and a second washer 24 and locking member 28 in the lower end portion16. A handle 30 is provided to grip the device, and triggers 34 and 38can be provided to operate the device during the implantation process. Aguide knob 35 can be operated to rotate the housing 14 and attachedlower end portion 16 to properly position the second washer 24. Alocking lever 32 can be provided to lock the device 10 on the bone afterthe first washer 20 and second washer 24 have been properly positioned.The locking lever 32 may be unlocked to allow repositioning of firstwasher 20 and second washer 24. A knob 37 can be provided to manuallyadvance the fastener and apply appropriate torque.

A slidable protective cannula or sheath 39 may be used to facilitateinsertion into the body and cover lower end portion 16. In FIG. 1 athere is shown a bone fastening device 10 having a protective cannula orsleeve 39 for shielding the housing 14 and lower end portion 16 duringthe insertion process. A grip 41 can be used to pull back the cannula 39prior to use. The housing 14, lower end portion 16 and guide knob 35 canbe detachable from the main body 12. Another housing 14, lower endportion 16 and guide knob 35, with another implant, can be attached forreuse of the main body portion 12.

There is shown in FIG. 2 an implant 40. The implant 40 comprises afastener having an elongated shaft 44 and a head 48. The fastenerengages the first washer 20 and the second washer 24 and locking member28. As shown in FIG. 3, the head 48 can have a convex surface 54 for usein engaging the first washer 20 as will be described below. Threads 58are provided on the shaft 44 for purposes of engaging the locking member28. Other engagement structure is possible. A pointed end 62 is providedfor piercing bone during the implantation process. Grooves or flutes 66provide space for bone chips to disperse during insertion into lockingmember 28 and to carry bone debris away from the point 62 as it isprogressing through the bone. Suitable structure such as hex opening 70is provided for engagement of the fastener 44 to apply compressive androtational forces during the implantation process. Depressions or othersuitable structure can be provided to permit a fastening device to gripthe head 48.

The second washer 24 and locking member 28 are shown in FIGS. 5-7. Thesecond washer 24 can have suitable structure such as serrations 80 forengaging the bone surface. Alternative structure is possible. The secondwasher 24 is pivotal with respect to the locking member 28. The lockingmember 28 can have suitable structure such as apertures 84. Cooperatingengagement structure such as clip 88 can be provided for extendingthrough apertures 89 in the second washer 24 and engaging the apertures84 such that the second washer 24 will engage the locking member 28. Aconvex surface 92 on the locking member 28 can cooperate with a similarconcave surface 96 on the second washer 24. The clip 88 can bepositioned in a suitable retaining groove 90 on the second washer 24. Anaperture 104 and slotted L-shaped groove 108 can be provided to engagecorresponding protrusions on the lower end portion 16 to secure thelocking member 28 to the lower end portion 16 of the fastening device10.

The first washer 20 is depicted in FIGS. 8-11. The first washer 20 canhave a concave surface 114 for cooperating with the convex surface 54 ofthe head 48 of the fastener 44. An elongated opening 118, which can bein the form of a tapered slot, permits the pivoting of the first washer20 relative to the fastener 44. The first washer 20 can have structurefor allowing the washer to be engaged by the fastening device 10. Thisstructure can be a circumferential groove 124 which can be engaged bycooperating flange structure on the fastening device 10. This will allowthe first washer 20 to be advanced toward the surface of the bone.Additional structure such as depressions 130 can be provided forengagement by the fastening device 10 to permit rotation of the firstwasher 20. This will assist in properly positioning the first washer 20.The first washer 20 can have an angled contact surface 136 which willpermit the first washer 20 to cooperate against bone surfaces such asfacets which present significant angles. Additional structure can beprovided for to promote engagement. This structure can includeserrations 140 on the contact surface 136. The opening 118 can expandwider in a fluted manner toward the contact surface 136 to permitgreater pivoting.

The manner of engagement between the fastener 44 and the first washer 20and second washer 24 and locking member 28 is depicted in FIGS. 12 a-c.The pivoting motion of the first washer 20 is shown. This washer cantilt approximately 30° from a transverse section through the screw axis.More or less is possible depending on the bone system that is beingfused. The second washer 24 is capable of tilting +45° to −20° from thetransverse to the screw axis. More or less is possible.

Suitable structure can be provided with the fastening device 10 forengaging the first washer 20. There is shown in FIG. 13 a collet 140although other holding structure is possible. The collet has distalcircumferential flanges 144 which engage the groove 124 on the firstwasher 20. Protrusions 148 are provided to engage the depressions 130 topermit the rotation of the first washer 20. Elongated slots 152 provideleaf springs 153 for creating a spring action on the lower lips 144 suchthat the collet 140 can engage and disengage from the first washer 20using moderate manual force.

The manner of engaging the first washer 20 and second washer 24 to thebone is shown in FIGS. 14-15. The locking member 28 is engaged to thelower end portion 16 in a suitable slot. Protrusions in the lower endportion 16 can engage the apertures 104 in the locking member 28. Thebone is shown schematically as a superior facet 160 and inferior facet164. The first washer 20 is engaged to the collet 140. The lower endportion 16 is positioned such that the second washer 24 rests againstthe inferior facet 164. The pivoting of the lower washer 24 relative tothe locking member 28 and lower end 16 permits the second washer 24 tomatch the incline portion 168 of the inferior facet 164. The collet 140is then lowered such that the first washer 20 engages the inclineportion 172 of the superior facet 160. The protrusions 148 engage thedepressions 130 such that rotation of the collet 140 will rotate thefirst washer 20 to properly position the first washer 20 relative to theincline portion 172 of the superior facet 160.

The installation of the fastener 44 is shown in the sequence of FIGS.16-18. The fastener 44 is held by a suitable engagement portion of thedevice 10 (not shown) and driven toward the superior facet 160. Thefastener 44 can be engaged such that the head 48 can be rotated and thepoint 62 can be driven into the facet 160. Flutes can be provided on thepointed end 62 to remove bone debris as the fastener 44 is rotated andpushed into the bone. In this manner, the fastener 44 will drill throughthe superior facet 160 and inferior facet 164. As the fastener 44 isadvanced through the bone, it will engage the locking member 28. Thethreads 58 will engage female threads in the locking member 28. Thefastener 44 will thereby be engaged to the locking member 28, as shownin FIG. 19. The collet 140 can then be removed, as shown in FIGS. 20 and21. The lower end portion 16 is then removed as the fastening device 10is removed, as shown in FIG. 22. This results in a completed implantacross the superior facet 160 and inferior facet 164, as shown in FIG.23.

A bone fixation device 10 as used during an implantation procedure isillustrated in FIGS. 24-26. The device 10 has an elongated housing 14 inthe general shape of a cannula. Within the housing is the collet 140.The collet 140 has structure for engaging the first washer 20. Anystructure is possible, however, the collet 140 in FIG. 24 has inwardlydirected circumferential holding flanges 144. The holding flanges 144engage the groove 124 on the first washer 20. The collet 140 further canhave protrusions 148 which engage the depressions 130 in the firstwasher 20. The first washer 20 is thereby held against movement out ofthe collet 140 and against rotation relative to the collet 140. Thespring force holding the first washer 20 in the collet 140 is such thata manual force can be used to remove the collet 140 from the firstwasher 20 after the first washer 20 has been secured to the bone.

The collet 140 is mounted in the housing 14 so as to be axially movabletherethrough. The collet 140 can have structure for slidably engaging aguide groove 222 or other suitable structure. The first trigger 34 canbe operated to move the collet 140 and first washer 20 through thehousing 14 from the position shown in FIG. 24 to the position shown inFIG. 25. When gear 230 is rotated the shaft 210 is pulled away by thethreaded end of the shaft 246. The first washer 20 will be seatedagainst the superior facet 160, and the second washer 24 will be seatedagainst the inferior facet 164. The guide knob 35 can be rotated toproperly position the second washer 24 if the orientation is notcorrect. The locking lever 32 can be operated to clamp the device to thefacet.

The helical gear 230 is then rotated by the action of the trigger 38,which causes the mostly slidable hexagonal or flat faced shaft 210 torotate. This rotates the extended threaded end of the shaft 246, whichis engaged to mating internal threads 250 on an interior surface of thecollet 140. The face of threaded end 246 includes structure for engagingthe fastener 44, such as a hexagonal tip. Rotation of the threaded end246 will thereby rotate and advance the fastener 44. The fastener 44will advance through the first washer 20, and through the superior facet160 and inferior facet 164 due to the drilling action created by theforward and rotational movement of the fastener 44. The fastener 44 willthen advance through the second washer 24 and into the locking member28. The threads 58 on the fastener 44 will engage cooperating threads onan inside surface of the locking member 28. The knob 37 can then beoperated to properly torque the implant 40 including to fully seatfastener 44 with locking member 28.

The invention provides numerous advantages over prior art pedicle screwfixation systems. As the bone joint segments, such as the superior facet160 and inferior facet 164, are compressed between the first washer 20and second washer 24, there are no internal threads in the bone to raisestresses within the bone. The threads 58 are only on the lower end ofthe shaft 44 such that these threads engage only the locking member 28and do not apply thread stresses to the interior of the bone. Also, asthe implant is tightened using the rotational force, conventionaltorqueing mechanisms can be applied such that a known compressive forceis applied to the joint. The first washer 20 and second washer 24 can beprovided with varied angled contact surfaces to variously fit differingbone geometries for joining bone segments other than the facets. Also,the amount of tilt in the first washer 20 and second washer 24 relativeto the fastener 44 can be adjusted depending upon the particular bonegeometry that is being fused, owing to the pivotal and polyaxial motionthat is permitted. The installation of the implant 40 is reversible. Thecompression of the implant washers 20 and 24 can be removed to allowrepositioning prior to fastener 44 insertion. Accordingly, the inventionprovides great variability and flexibility, in addition to ease, controland consistency of installation.

The various components of the invention are constructed withconstructions of surgical grade plastics or metal, such as titanium.Different dimensions of the various components of the invention arewithin the scope of the invention.

This invention can be embodied in other forms without departing from thespirit or essential attributes thereof and, accordingly, referenceshould be had to the following claims rather than the foregoingspecification as indicating the scope of the invention.

1. An implant for bone arthrodesis, comprising: a fastener with anelongated shaft having a head at one end and a threaded portion at theopposite end terminating in a bone-piercing point; a first washer havingstructure for engaging the head of said shaft so as to be polyaxiallypivotable with respect to said head; and a locking member comprising anut having threads that cooperate with the threaded portion on saidshaft, said locking member having a second washer pivotally engagedthereto by a clip.
 2. A system for performing bone fixation, comprising:an implant for bone fixation, comprising a fastener with an elongatedshaft having a head at one end and a bone-piercing point at the oppositeend; a first washer having a first structure for engaging the head ofsaid shaft so as to be polyaxially pivotable with respect to said head;and a locking member having a second structure for engaging said shaft,said locking member having a second washer pivotally engaged thereto: abone fixation device, comprising an elongated cannula having a colletfor detachably engaging said first washer and for advancing the firstwasher, and a third structure for engaging said fastener and foradvancing the fastener through the collet and through the first washer;said bone fixation device further comprising a lower end portionextending from said cannula, said lower end portion having a fourthstructure for detachably engaging said locking member, said fastener,first washer, and locking member being aligned such that said advancingfastener will advance through said first washer, through said bone, andinto said locking member.
 3. A method for performing bone fixation,comprising the steps of: providing an implant for bone fixation,comprising a fastener with an elongated shaft having a head at one endand a bone-piercing point at the opposite end; a first washer having afirst structure for engaging the head of said shaft so as to bepolyaxially pivotable with respect to said head; and a locking memberhaving a second structure for engaging said shaft, said locking memberhaving a second washer pivotally engaged thereto; providing a bonefixation device, comprising an elongated cannula having a collet fordetachably engaging said first washer and for advancing the firstwasher, and a third structure for engaging said fastener and foradvancing the fastener through the collet and through the first washer;a lower end portion extending from said cannula, said lower end portionhaving a fourth structure for detachably engaging said locking member,said fastener, first washer, and locking member being aligned such thatsaid advancing fastener will advance through said first washer, throughsaid bone, and into said locking member; positioning said bone fixationdevice with said bone between said cannula and said lower end portion;operating said device to advance said first washer to said bone; andoperating said device to advance said fastener through said firstwasher, said bone, and said locking member.
 4. A system for performingbone fixation, comprising: an implant for bone fixation, comprising afastener with an elongated shaft having a head at one end and abone-piercing point at the opposite end; a first washer having a firststructure for engaging the head of said shaft; and a locking memberhaving a second structure for engaging said shaft; a bone fixationdevice, comprising an elongated cannula having a third structure fordetachably engaging said first washer and for advancing the firstwasher, and a fourth structure for engaging said fastener and foradvancing and rotating the fastener through the first washer; said bonefixation device further comprising a lower end portion extending fromsaid cannula, said lower end portion having a fifth structure fordetachably engaging said locking member, said fastener, first washer,and locking member being aligned such that said advancing fastener willadvance through said first washer, drill through said bone, and advanceinto said locking member.
 5. The system for performing bone fixation ofclaim 4, wherein said elongated cannula is detachable from said bonefixation device, whereby a replacement cannula having another implantcan be attached to said device.
 6. A method for performing bonefixation, comprising: providing an implant for bone fixation, comprisinga fastener with an elongated shaft having a head at one end and abone-piercing point at the opposite end; a first washer having a firststructure for engaging the head of said shaft; and a locking memberhaving a second structure for engaging said shaft; providing a bonefixation device, comprising an elongated cannula having a thirdstructure for detachably engaging said first washer and for advancingthe first washer, and a fourth structure for detachably engaging saidfastener and for advancing and rotating the fastener through the firstwasher; said bone fixation device further comprising a lower end portionextending from said cannula, said lower end portion having a fifthstructure for detachably engaging said locking member, said fastener,first washer, and locking member being aligned such that said advancingfastener will advance through said first washer, and advance into saidlocking member; positioning said bone fixation device with said bonebetween said cannula and said lower end portion; operating said deviceto advance said first washer to said bone; and operating said device toadvance and rotate said fastener through said washer, drill through saidbone, and move into said locking member.